Production of middle distillates



March 1, 1960 E. M. GLADROW EFAL 2,927,072

PRODUCTION OF MIDDLE DISTILLATES v Filed July 51, 1956 FILTER AN D/OR SETTLER FRACTIONATOR REACTOR HEAT EXCHANGER Elroy M. Glodrow P B. Mason By Attorney Unitfd W 8. Patent PRODUCTION OF MIDDLE DIS'IYILLATES Elroy Merle Gladrow, Baton Rouge, Ralph Burgess Mason,.Denham Springs, and Charles'Newton Kimberliu, Jr., and William Floyd Arey, Jr., Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application July 31,. 1956, Serial No. 601,180 "6 Claims. (Cl. 208-46) The present invention relates to the processing of hydrocarbon oils to produce higher-boiling hydrocarbons, and more particularly to a combination process for converting naphthas boiling in the gasoline range into middle distillate fractions suitable as heating oils, jet fuels, tr-actor fuels and the like.

The principal object of the present invention is to provide a process for converting low octane or unstable naphthas and other lowoctane components of gasoline into material of higher value and higher boiling range. With the introduction of high compression ratio automobile engines the octane requirements of gasoline has been steadily increasing; and this has resulted in the narrowing of the choice of'constituents that can be used as high octane gasoline blending agents. Much virgin naphtha and naphtha resulting from the catalytic cracking. from gas oil, hitherto employable in gasoline blends suitable for engines of moderate compression ratios, can no longer be used for this purpose. Similarly, refinery processes suchas fluidized coking of heavy oils and residua and visbreaking produce naphthas that are unstable, with resultant sludge forming. characteristics, and are of too high sulfur content for satisfactory use.

Concomitant with the accumulation of these naphtha streams and products in the refineries, there has grown in'recent years increased demands for hydrocarbons boilingin the middle distillate range of from about 300 to 750 F. The rapid growth of heating oil installations both in the United States and abroad, and the increased .virgin crude oil or from mixtures of virgin and cracked products. The phenomenal increasein demand for dis:

tillate fuels brought-about by "the factors enumerated above, as well as the increase in diesel fuel requirements, has presented, therefore, .a serious problem to the oil refining industry. 7

Middle distillates, or distillatefuels, usually boil in the range of about 350-750 F., the so-called heater oils boiling chiefly in the range of 350-550" F., while diesel fuels boil at about 400-650 F. It is desirable to have these products of low sulfur content and low sludging characteristics.

In accordance with the presentinvention, refinery imbalances between gasoline and heating oil demands and stocks are restored by catalytic conversion of naphtha fractions into middle distillates. This is in a sense the reverse of the hitherto trend: of petroleum refining where the gasoline fraction was the desired product, and where low grade gasoline fractions were upgraded to high antiknock material by such processes as reforming or isomerization. The present invention involves principally conversion of the naphtha into middle distillate by catalytic condensation reaction involving formation and reaction of an olefinic intermediate, if a completely saturated naphtha, such as casinghead or virgin naphtha is initially fed into the process. In brief compass, it has been found that high yields of high quality low gravity middle distillates may be obtained by the catalytic conversion of low quality naphthas in the presence of. a solid catalyst of the mixed oxide type, such as a magnesia-silica or a silica alumina catalyst at elevated temperatures and pressures. In one embodiment ofthe present invention naphtha is thermally cracked to a moderate or relatively low degree of conversion, forming substantial quantities ofolefins which are then passed to the catalytic conversion zone. In another embodiment low grade naphtha, such ascatalytic naphtha or coker naphtha is mixed in minor amounts with virgin or casing head naphtha prior to conversion; Though thepresence of olefins is a necessary intermediate; there is a disappearance of naphtha, and it is probable that under the reactionconditions, polymerization of olefins is accompanied by substantial alkylation of olefinic naphtha with the saturated naphtha. In still another embodiment, wherein unstable naphthas such as visbreaker naphtha or fluid coker naphtha are being processed, no virgin naphtha need be concomitantly processed.

The invention Will be more readily understood when read in conjunction with the more detailed description hereinafter wherein reference will be made to theaccompanying drawing which is a diagrammatic illustration ofa preferred embodiment of the invention. Turning now to the drawing, a naphtha feed comprising low quality low octane naphtha, such as virgin naphtha, casing head naphtha or other substantially parafiinic or saturated naphtha is passed via line 2 to thermal cracking zone 4. Conditions within zone 4 are maintained such as to insure relatively low feed conversion and high olefin selectivity. Preferred conditions are relatively mild conditions of temperature and pressure. Thus it is preferred to operate the cracking zone at temperatures in the range of 950 to 1150 F. at pressures in the range of 50 to 400 p.s.i.g. At times, however, it may be expedient to operate the cracking zone at the pressure of the subsequent part of the system because a compressor will be required between the cracking zone and the reactor system if the twoare to operate at their re spective optimum pressures. When it is desired to strike such a balance and operate with a minimum of compression equipment, the cracking zone pressures may be as high as 1200 p.s.i.g. The nature of the cracking operation is such that for the sameconversion the feed rate varies over wide limits with variations in temperature and pressure. In general the liquid feed is maintained in the range of 0.3 to 6 liquid volumes per volume of cracking zone. Although expressed as liquid rate, it is understood that with naphtha feeds the conditions in the cracking zone are essentially those of vapor phase.

The effluent from cracking zone 4 is passed via line 6 togas separator .10. Low boiling cracked gases are withdrawn through line 11, while the liquid cracked naphtha now containing a substantial amount of olefins, and which naphtha may have a product bromine number of 30 50, is passed via line 12 and heat exchanger 14 to naphtha conversion zone 20.

The operating conditions of zone 20 to obtain good yields are critical. It was found to be essential to employ and maintain a liquid phase operation. A heavy build up of tar on the catalyst normally occurs, and only by maintaining a liquid phase was it found possible coittinuously to remove polymer and tar on the catalyst as 3 formed, thereby prolonging catalyst life and increasing the extent of condensation of the naphtha constituents. The desired liquid phase condition may be achieved by various means. One such and 'preferred is maintenance of an up-flow operation. Recycle of a portionof the higher boiling component is another.

Within zone 20 there is maintained a naphtha conversion catalyst of the oxide or mixed oxide type, preferably a silica-alumina or a silica-magnesia catalyst of the type conventionally employed for cracking hydrocarbons catalytically. These are well-known per se, as is also their method of preparation. If desired, the catalyst may be activated with minor amounts of known activating agents such as AlCl BE. and the like. Reaction conditions within conversion zone 20 include high pressures, above about 600 p.s.i.g., and preferably above about 750 p.s.i.g. up to 3000 p.s.i.g. and higher. Temperatures in the range of about BOO-750 F. and liquid feed rates of 0.2 to 2 v./v./hr. may be used.

, Though a fixed bed catalyst may be maintained within reactor 20, frequent reactivation would be necessary to maintain the bed at a high conversion level. A more satisfactory operation is the maintenance of the catalyst in suspension in the liquid phase operation. About 1% to 25% catalyst on the total feed, and preferably about 3% to may be employed. The upflowing naphtha stream admitted through line 16 maintains the catalyst in constant suspension.

The reaction product is withdrawn from the top of reactor 20 by line 21 and passed to product filtrationsettling zone 34. Filtered product is passed via line 24 to product fractionator 26. The desired middle distillate fraction is withdrawn through line 30, while unreacted naphtha may be recycled through line 28 to the cracking zone or, if desired, in part to conversion zone 20 through lines 28 and 46.

The catalyst separated in filtration zone 34 is withdrawn downwardly through line 36 and passed to a fluidized solids regeneration zone 40. In this zone, the catalyst to be regenerated is maintained as a fluidized bed of solids by an upflowing regeneration gas stream, such as air, admitted through line 48. The regeneration is carried out at temperatures of about 900 to 1200 F., and the hot regenerated catalyst passes downwardly through standpipe 50 and is passed via aerated lines 42 and 44 through heat exchanger 14 to lockhopper 22, whence it is returned to the reactor 20 through line 18. The fluid solids transfer is effected through a gas lift by an inert gas, such as nitrogen, steam, natural gas or the oxides of carbon, being introduced through line 52 and removed by line 54.

The process of the present invention may be modified in many features without departing from its spirit. Thus, if the naphtha to be converted is appreciably olefinic, with a bromine number of about 60 or higher, the thermal cracking step may be omitted and the naphtha passed directly into conversion Zone 20 through lines 2, 3 and 12. Similarly, it may be desirable to add mixed streams of olefinic and substantially paraffinic low octane naphthas directly into the conversion zone, for the resulting middle distillate is formed essentially by alkylation as well as polymerization reactions. On the other hand, it may also be desirable to add olefinic naphthas as such, or as the sole feed, to the thermal cracking zone. This is particularly true where these naphthas are unstable.

Besides the catalysts named, other suitable oxide catalysts are natural clays, acid-treated clays, and fluoridetreated clays. However, a diatomaceous earth catalyst impregnated with phosphoric acid, a well-known polymerization catalyst, was not found to be suitable for this service.

Fractions boiling higher than the middle distillate may be removed through line 32 and may also be recycled to the thermal cracking zone to make further middle distillate.

4 a The process of the present invention may be more clearly illustrated in the following specific examples.

Exa'inple 1 A coker naphtha having a boiling range of 170 to 400 F. and a bromine number of 106 was agitated in a shaker autoclave with a commercial silica alumina catalyst under difierent conditions of temperature. Also a similar test was made at one temperature condition with a feed comprising 29% by weight of the same coker naphtha and 79% of virgin naphtha. Results of these experiments are set forth below:

[3-liter shaker autoclave unit, 6 hours operation, 20 wt. percent silicaaluminaJ 29% Coker ap h., Feed Coker N aptha 71% Lt. Virgin Naphtha Temp, F 450 600 750 750 Pressure, P.s.l.g 125 350 900 1,

Feed Feed Liquid Prod. Dist., Wt.

Percent:

ESP-350 F 78 37. 6 20. 8 60. 3 93.6 83. 4 350-430" F 22 17. 4 50. 9 18. 7 6. 4 6. 6 430 Bottoms 45. 0 28. 3 21.0 1 10. M34. 5)

Inspections, Total Prod:

Gravity 49 39 46 54 Bromine No 106 32 24 9 31 4 1 Value in parentheses is on coker naphtha basis.

A substantial increase in the 430 F. plus product is noted. Under conditions of the test the product distribution and yield change with temperature, but comparison of column 4 with column 3 demonstrates greater selectivity in presence of an added non-olefinic naphtha, i.e., more middle distillate was made than would be predicted or accounted for on the basis of the coker naphtha con tent alone.

Example 2 The same feed stock was passed in a continuous op.-

eration over a fresh charge of the silica-alumina catalyst with results as tabulated below:

[Coker naphtha feed (170400 F. boiling range, 106 Br. No), 400 cc.

silica-alumina catalyst, feed rate 1 v./v./hr.]

Temperature, F. 450 600 Run, Hours 12-175 Product Dist, Wt; Percent:

IB 0 F 1,015 Bottoms 1. 3

Thus, substantial yields of 350-650 F. product are demonstrated with only small amounts of extremely high boiling 850 F. plus product.

Example 3 Temperature, F--- 450 500 Catalyst SiO:AlrO; UOP" Slot-A110; UOP

Tot. Vol. Feed Processed/Vol.

Cat 18 30 21 33 58 70 60 84 Vol. Percent 350 F.

Product 25 24 18 17 22 23 19 19 Br. No. of Naphtha Residue 44 63 65 43 44 54 04 Catalyst l3Alz0;87SiO| UOP" Vol. of feed processed/vol. cat 16 Br. N o. of N aphtha Residue. 12 41 Vol. Percent 350 F. Yield:

On feed 17 10 Total (first plus second pass) 81 26 These data show a consistent advantage of higher yields of middle distillate over the silica-alumina catalyst.

The recycle feature which gave added yield can be achieved, or at least in part, by employing partial condensation and recycling the uncondensed low boiling compounds.

Example 4 A thermal cracking coil was installed on the upstream side of a catalytic converter and was operated at 1000 F. and 1025 F. and 400 p.s.i.g. with a virgin naphtha feed which had essentially no olefins and gave negligible conversion when passed over the catalyst without pretreatment. The catalytic section was operated at 400 p.s.i.g. and 600 F. with the commercial silica-alumina preparation used in the preceding experiments. The data are:

[Baton Rouge virgin naphtha, 1 liq. v./v./Hr., 400 p.s.i.g., 600 F.,

silica-alumina catalyst.]

Feed Cracking Coil Temp.,F

Without With Cat. Treatment Treatment 1,000 1,025

Only

Vol. Percent 350 F.

Product 0 0 15 17 This demonstrates the feasibility of the two-stage process involving cracking and condensation. Thus, in the absence of olefins, thermal and catalytic treatment of the virgin naphtha gave no product.

Example 5 Typical inspection data on middle distillate samples from various feeds and conditions of operation are summarized as follows:

Catalyst Silica-Alumina UOP" Feed Ooker Catalytic Catalytic Naph. aph. Naph.

Feed Rate, V./V./Hr 0.5 0.51 1 1 1 Temperature, F--. 600 600 500 500 50 Pressure, P.S.l.g 800 800 800 800 Vol. Percent 350 F.+Product 23 10 19. 9 18. 6 1 10. Inspections 350050 F. Prod.

Gravity, A.P.I 35. 4 331 33. 2 35. 9 35. Bromine No 66 72: 68 109 86. Aniline Pt., F 821 95. 2 97 86. Flash Point, Tag. F 144 14 7 Second pass operation with unconverted naphtha from first cycle.

The middle distillate under each set of conditions has a high flash point and is suitable for use as a heating oil. Also, it is possible to use the lower boiling components as jet fuel. The high olefinicity of the UOP product as against the SiO -Al- O product is to be noted. High olefinicity is an undesirable property in middle distillates, particularly those that are to be used as fuels, for they are readily susceptible to oxidation and sludging.

What is claimed is:

1. An improved process for converting paraffinic low octane naphtha into middle distillates which comprises passing said naphtha to a thermal cracking zone, maintaining a relatively low degree of conversion in said zone, forming olefinic hydrocarbons in said zone, pass-ing efilucnt from said cracking zone to an olefin conversion zone, maintaining a mixed oxide catalyst selected from the group of magnesia-silica and silica-alumina in said zone, maintaining a pressure in the range of from about 600 to 3000 p.s.i.g. and a temperature of about 300 F. to 750 F. in said zone, further maintaining a liquid phase operation therein, keeping said catalyst suspended in said liquid phase, polymerizingand alkylating said efiluent in said conversion zone, and recovering good yields of middle distillates.

'2. The process of claim 1 wherein 1% to 25% of catalyst, based on feed, is maintained in said conversion zone.

3. The process of claim 1 wherein said thermal cracking operation is carried out at pressures in the range of about 50 to 400 p.s.i.g. and temperatures of about 950- 1150" F.

4. An improved process for making middle distillates from lower boiling hydrocarbons which comprises passing an olefinic naphtha into a conversion zone, maintaining a liquid phase operation therein, maintaining an alumina-silica catalyst therein, maintaining a temperature of from about 300-750 F. and pressures of about 600- 3000 p.s.i.g., and feed rate of 0.2 to 2.0 v./v./hr. therein, polymerizing and alkylating said olefinic naphtha in said conversion zone, and recovering high yield of middle distillate.

5. The process of claim 4 wherein virgin naphtha is passed into said zone in admixture with an olefin comprising naphtha.

6. The process of claim 1 wherein said liquid phase operation is maintained by recycle of a higher boiling component.

References Cited in the file of this patent UNITED STATES PATENTS 2,067,030 Peski Jan. 5, 1937 2,197,861 Hyman Apr. 23, 1940 2,310,327 Sweeney Feb. 9, 1943 2,328,756 Thomas Sept. 7, 1943 2,333,625 Angeli Nov. 9, 1943 2,418,028 Haensel Mar. 25, 1947 2,435,708 Byrns Feb. 10, 1948 2,543,016 Grosse Feb. 27, 1951 2,733,285 Hammer Jan. 31, 1956 2,753,382 Hamner July 3, 1956 2,779,750 Fuqua Jan. 29, 1957 

1. AN IMPROVED PROCESS FOR CONVERTING PARAFFINIC LOW OCTANE NAPHTHA INTO MIDDLE DISTILLATES WHICH COMPRISES PASSING SAID NAPHTTHA TO A THERMAL CRACKING ZONE, MAINTAINING A RELATIVELY LOW DEGREE OF CONVERSION IN SAID ZONE, FORMING OLEFINIC HYDROCARBONS IN SAID ZONE, PASSING EFFLUENT FROM SAID CRACKING ZONE TO AN OLEFIN CONVERSION ZONE, MAINTAINING A MIXED OXIDE CATALYST SELECTED FROM THE GROUP OF MAGNESIA-SILICA AND SILICA-ALUMINA IN SAID ZONE, MAINTAINING A PRESSURE IN THE RANGE OF FROM ABOUT 600 TO 3000 P.S.I.G. AND A TEMPERATURE OF ABOUT 300*F. TO 750*F. IN SAID ZONE, FURTHER MAINTAINING A LIQUID PHASE OPERATION THEREIN, KEEPING SAID CATALYST SUSPENDED IN SAID LIQUID PHASE, POLYMERZING AND ALKYLATING SAID EFFLUENT IN SAID CONVERSION ZONE, AND RECOVERING GOOD YIELDS OF MIDDLE DISTILLATES. 